It has already been suggested to provide members of copier, facsimile machine, printer, such as magnetic drum, doctor blade, scrappers, scraping blade, rollers, photoconductive imaging member, with specific top layer or intermediate layers.
For example U.S. Pat. No. 6,074,791 disclose a photoconductive imaging member comprised of a supporting substrate, a hole blocking layer thereover, a photo generating layer and a charge transport layer.
Tests have shown that the top layer of the members of printer in contact with toner particles has to be accurately selected in order to have the best life time, i.e. the longer working of the printer.
It has now been discovered that by using members provided with a top layer containing spherical particles with a particle size lower than 100 xcexcm, it was possible to improve the quality of the copies of a copier and the life time of said members. For example, it has been discovered that by using a magnetic drum provided with such a top layer, it was possible to ensure good copies after more than 40,000 copies and even more. It has also been observed that the efficiency of the toner transfer was improved when using member of the invention, especially a magnetic drum of the invention.
The invention relates to a member for a printer, a fax machine, a copier or a toner cartridge, in which said member has a face in contact with toner particles, said face being provided with a top layer in contact with toner particles, said cop layer comprising substantially spherical particles with a Mohs hardness of more than 3 or equal to 3, advantageously more than 4, preferably more than 4.5, most preferably comprised however between 3 and 7 and an average particle size lower than 100 xcexcm, advantageously lower than 50 xcexcm, preferably lower than 40 xcexcm.
Substantially spherical particles means in the present specification particles having a spherical shape, a substantially spherical body provided with one or more (for example two) recesses, such a form similar to an apple, particles having an ovoid shape, shape having a ratio volume/surface comprised 1:4.2 and 1:2, etc.
Substantially spherical particles with a Mohs hardness of more than 3 or equal to 3 means substantially spherical particles having as such a Mohs hardness of more than 3 or equal to 3, spherical particles having a core with a Mohs hardness of more than 3 or equal to 3, as well as particles provided with an outer coating having a Mohs hardness of more than 3 or equal to 3. Preferably, the particle as such or its core has a Mohs hardness of more than 3 or equal to 3.
According to an embodiment, at least 50% of the substantially spherical particles with a Mohs hardness of more than 3 or equal to 3 have advantageously a particle size distribution factor at 80% of less than 1. Most preferably the substantially spherical particles with a Mohs hardness of more than 3 or equal to 3 and having a particle size greater than 25 xcexcm have a distribution factor at 80% lower than 1, preferably lower than 0.8. The distribution factor at 80% is equal to:
xe2x80x83(xcfx8680%xe2x88x92xcfx8620%)/[(xcfx8680%+xcfx8620%)/2]
in which
xcfx8620% is the maximum diameter of the particles fraction corresponding to 20% by weight of the particles, the particles of said fraction having a diameter or particle size lower than xcfx8620% 
xcfx8680% is the maximum diameter of the particles fraction corresponding to 80% by weight of the particles, the particles of said fraction having a diameter or particle size lower than xcfx8680% 
Preferably, at least 50% of the substantially spherical particles with a Mohs hardness of more than 3 or equal to 3 have a particle size distribution factor at 90% of less than 1, advantageously of less than 0.8, preferably of less than 0.5, most preferably of less than 0.3. A small particle size distribution factor means that substantially all the particles have a diameter corresponding substantially to the average diameter. This is advantageous in order to obtain a layer having a substantially constant thickness. Most preferably the substantially spherical particles with a Mohs hardness of more than 3 or equal to 3 and having a particle size greater than 25 xcexcm have a distribution factor at 90% lower than 1, preferably lower than 0.8, most preferably lower than 0.5, such lower than 0.3.
The distribution factor at 90% is equal to:
(xcfx8690%xe2x88x92xcfx8610%)/[(xcfx8690%+xcfx8610%)/2]
in which
xcfx8610% is the maximum diameter of the particles fraction corresponding to 10% by weight of the particles, the particles of said fraction having a diameter or particle size lower than xcfx8610% 
xcfx8690% is the maximum diameter of the particles fraction corresponding to 90% by weight of the particles, the particles of said fraction having a diameter or particle size lower than xcfx8690%.
According to an embodiment, the top layer comprises various different fractions of substantially spherical particles with a Mohs hardness of more than 3 or equal to 3. For example, the top layer comprises substantially spherical particles with a bi-modal distribution. The top layer comprises for example a mixture of substantially spherical particles, a first fraction of which having an average diameter greater than 30 xcexcm, and a second fraction of which having an average diameter lower than 20 xcexcm, the weight ratio first fraction/second fraction being comprised between 1:20 and 20:1, advantageously between 1:10 and 10:1, preferably between 1:4 and 4:1. The presence of the two fractions can be seen for example when plotting a particle size curve, due to the presence of two visible peaks corresponding substantially to the average particle size of the second fraction and the average particle size of the first fraction.
When using a mixture of larger particles (such as particles with a particle size greater than 20 xcexcm, preferably with an average particle size greater than about 30 xcexcm), it is advantageous to add to the mixture some smaller particles (such as particles with a particle size lower than about 10 xcexcm) so as to fill the inter space formed between the larger particles. This is particularly advantageous when the support or substrate to be provided with a top layer is not plane (is curved, for example cylindrical).
Possibly, the top layer can contain particles with a Mohs hardness of less than 3, for example substantially spherical particles with a Mohs hardness of less than 3, fibres, filaments, fabrics, metallic powders (copper, zinc, tin, iron, aluminium, etc.), metallic fibres, carbon particles, carbon black, carbon fibres, etc. Preferably, the top layer is however free or substantially free of particles with a Mohs hardness of less than 2.
According to a detail of an embodiment, the top layer comprising substantially spherical particles with a Mohs hardness of more than 3 or equal to 3 is a layer comprising a binder for binding the spherical particles in the layer, said layer having a top face at which a portion of substantially spherical particles with a Mohs hardness of more than 3 or equal to 3 is provided with a binder coating with a thickness of less than 50 xcexcm, advantageously lower than 30 xcexcm, preferably lower than 20 xcexcm, most preferably of less than 10 xcexcm.
Preferably, the top layer comprising substantially spherical particles with a Mohs hardness of more than 3 or equal to 3 is a layer comprising a binder for binding the substantially spherical particles in the layer, said layer having a top face at which a portion of spherical particles with a Mohs hardness of more than 3 or equal to 3 is substantially free of binder.
The binder is advantageously a synthetic binder, advantageously a binder being substantially stable at temperature above 50xc2x0 C., advantageously above 800xc2x0 C. preferably above 100xc2x0 C., for example stable at temperature comprised between 130xc2x0 C. and 300xc2x0 C., or even more. Such binder is for example polyurethane, thermoplastic polyurethane, a polyester, a polyester polyurethane, silane, a fluorosilane, a fluorosiloxane, polysiloxane, polypropylene, polyethylene, epoxy resin, rubber, teflon, PVC, polyphenylene oxide, polysulfone, polyamide, polyimide polymer, etc. and mixtures thereof. The binder can have a foam structure, but has preferably no foam structure or substantially no foam structure. Advantageously the resin has some electrical conductive properties and is preferably considered as electrically conductive.
The top layer has advantageously a resistance against abrasion measured by the ASTM-1938 abrasion test of less than 0.1 g. The preparation of polyurethane films, bands or layers (conductive or not) can be made by using the methods disclosed in U.S. Pat. Nos. 3,933,5448; 3,830,656; 5,855,820; EP 0 786 422 and/or EP 0 337 228, the content of which is incorporated herewith by reference. When the layer has to be non conductive, no conductive materials are added in the process of U.S. Pat. Nos. 3,933,5448; 3,830,656; 5,855;820 EP 0 786 422. Advantageously, the polyurethane is however a thermoplastic polyurethane.
For having an easy preparation of the top layer, the binder is advantageously selected form the group comprising curable binders, such as heat curable binders, radiation curable binder, etc. The top layer is advantageously prepared from a solution or dispersion containing the curable binder, said solution or dispersion being an organic solvent based solution or dispersion, but preferably an aqueous solution or dispersion. The dispersion is advantageously free of enmulgators or emulsifiers.
The top layer has advantageously an electrical surface resistivity of less than 1013xcexa9 per square, preferably lower than 105xcexa9 per square, most preferably lower than 103xcexa9 per square, for example 102xcexa9 per square, 10xcexa9 per square or even less.
The top layer is advantageously attached or bond to a substrate or support with interposition of one or more intermediate layers, such as an elastic layer, a conductive layer, a layer with a high electrical resistance, such a layer having for example a surface electrical resistance of more than 1010xcexa9 per square, advantageously more than 1012xcexa9 per square, preferably more than 1013xcexa9 per square, most preferably more than 1014xcexa9 per square.
The top layer has for example a thickness of less than 500 xcexcm, advantageously of less than 200 xcexcm, preferably of less than 100 xcexcm, such as less than 50 xcexcm, for example 40 xcexcm, 30 xcexcm, 20 xcexcm. Preferably, the top layer has a minimum thickness of about 10 xcexcm.
According to a preferred embodiment, the top layer has an average maximum thickness corresponding substantially to the average particle size of the spherical particles with a Mohs hardness of more than 3 or equal to 3 or an average thickness corresponding substantially to the maximum particle size of the substantially spherical particles.
The top layer is advantageously electrically conductive. For example, the spherical particles are electrically conductive. For example, the spherical particles are provided with an electrically conductive coating having a thickness of less than 50 xcexcm, advantageously of less than 30 xcexcm, preferably less than 20 xcexcm, most preferably less than 10 xcexcm, such as less than 5 xcexcm, for example 2 xcexcm or even less (1 xcexcm or even less). The substantially spherical particles can possibly be only partly coated.
According to a specific embodiment, the top layer comprises binder and spherical particles with a Mohs hardness of more than 3 or equal to 3 and an average particle size lower than 100 xcexcm, the volume ratio binder/substantially spherical particles with a Mohs hardness of more than 3 or equal to 3 and an average particle size lower than 100 xcexcm being lower than 1, advantageously lower than 0.7, preferably lower than 0.5.
For example, the weight content of substantially spherical particles with a Mohs hardness of more than 3 or equal to 3 and with a particle size of less than 100 xcexcm in the top layer is comprised between 1% and 30%, advantageously between 1.5% and 20%, preferably between 2% and 15%, most preferably between 5% and 12%.
The spherical particles have an apparent density which can be higher than 1, lower than 1 or possibly equal to about 1.
The top, laxer comprises advantageously a binder and spherical particles with a Mohs hardness of more than 3 or equal to 3 and an average particle size lower than 100 xcexcm, said the spherical particles having an apparent density lower than, higher than or equal to the density of the binder.
The member of the invention is advantageously selected from the group consisting of a photoconductive imaging member, a doctor blade, a scraping blade, a roller, a magnetic drum, an OPC, a wiper blade, etc.
Examples of spherical particles adapted to be used in the member of the invention are spherical glass particles or beads, alumina particles, quartz particles, particles covered with a layer having a Mohs hardness of more than 3 or equal to 3, for example spherical plastic particles provided with an outer coatings having a hardness of more than 3 or equal to 3, spherical glass or siliceous particles provided with a silane or fluorosilane coating. Examples of suitable particles are particles used in the manufacture of recording magnetic tape or support, such as particles of calcium carbonate, for example prepared by precipitation. Particles suitable to be used are rounded particles, the mechanical rounding being possibly a natural rounding due to the sea.
The particles can be hollow particles (so as to decrease the density of the particles), filled with a gas or possibly filled with a material, such a resin, etc.) or common spherical particles (not hollow).
The member of the invention can possibly be only partly coated, or can be coated with a top layer having a variable thickness.
The invention relates also to a machine selected from the group consisting of a copier, facsimile machine, printer, laser printer and toner cartridges, said machine comprising at least a face intended to be in contact with toner particles, said face being provided with a top layer in contact with toner particles, said top layer comprising substantially spherical particles with a Mohs hardness of more than 3 or equal to 3 and an average particle size lower than 100 xcexcm.
The machine of the invention comprises preferably one or more members of the invention as disclosed here before in the present specification.
The invention further relates to a support to be attached to a member of a printer, a fax machine, a copier or a toner cartridge, in which said support has a first face intended to be attached to said member and a second face opposite to said first face and intended to be in contact with toner particles, said second face being provided with a top layer in contact with toner particles, said top layer comprising substantially spherical particles with a Mohs hardness of more than 3 or equal to 3, advantageously higher than 4, preferably higher than 4.5, most preferably comprised between 3 and 7, and an average particle size lower than 100 xcexcm, advantageously lower than 50 xcexcm, preferably lower than about 30 xcexcm. Possibly, the support is the top layer. However, preferably, the support comprises a substrate supporting the top layer. The top layer of the substrate is preferably a top layer as disclosed for the member of the invention.
The support is advantageously a support to be attached, for example to be glued on a member selected from the group consisting of a photoconductive imagine member, a doctor blade, a scraping blade or element, a roller, a magnetic drum.
The first face is advantageously provided with glue, said glue being preferably protected by a siliconized paper or sheet, or any other material which can be removed from the support before and/or during its gluing on an element of a copier, printer, faximile machine, laser printer, etc.
The invention still further relates to a printing process using toner particles and using a machine of the invention, i.e. a machine comprising a member of the invention. The printing process in which toner particles are transferred on a member selected from the group consisting of photoconductive imaging member and magnetic drum, has the improvement that toner particles are transferred on a top face of said member, said top face being provided with a top layer in contact with toner particles, said top layer comprising substantially spherical particles with a Mohs hardness of more than 3 or equal to 3, advantageously more than 4, preferably more than 5, and an average particle size lower than 100 xcexcm, advantageously lower than 50 xcexcm.
It has also been observed that when using a magnetic drum provided with a top layer of the invention, the life time of the doctor blade, OPC and wiper blade was increased. The wearing of the doctor blade, wiper blade and OPC was reduced.
The top layer in said process is advantageously of the type disclosed in the member of the invention.